In 181 patients resuscitated from cardiac arrest, the prevalence and duration of coma were registered and related to the site of occurrence of cardiac arrest, cardiac rhythm during arrest, age and clinical outcome of the patients. Coma was most frequent after cardiac arrest outside the hospital, as 84% of these patients were comatose for more than 1 h and 56% for more than 24 h; the corresponding values for patients with cardiac arrest in general wards were 63% and 30%, respectively, and for patients with cardiac arrest during ambulance transport, 80% and 44%. Permanent brain damage was extremely rare if the coma lasted less than 6 h (1 out of 62 patients), and relatively rare with a coma duration between 6 and 24 h (5 out of 34 patients). Of the patients, 85 remained comatose for more than 24 h and only 7 of them were discharged alive, all with cerebral impairment of a severity increasing with the duration of the coma. None regained consciousness after more than 7 days' coma, and a total of 80 patients died in coma, 20 with signs of cerebral death. Older patients were more vulnerable to coma than younger ones, but coma as such was not more frequent. We found no differences in coma after asystole and ventricular fibrillation. Problems concerning the selection of patients who have a chance of survival, although comatose after cardiac arrest, are discussed.